Fuels, particularly those used in heavy fuel engines, contain increasingly large quantities of sulfur. At the same time the conditions of operation become more strict.
It has become necessary to add to lubricant oils different additives that improve their properties. Among such additives are found the detergents, the dispersants, additives against wear and extreme pressure, and additives that contribute a reserve of basicity.
The detergent and dispersant properties of a lubricant correspond to its ability to maintain in suspension the impurities and incombustible substances in the hot parts of the engine by its detergent action, but equally in the cold parts by its dispersant action. The fixation of these particles in the form of varnishes or lacquers is thus prevented.
The part played by the additives with a reserve of basicity consists in fighting the acidity induced in the engines by the combustion of the sulfurized organic derivatives contained in the engine fuels and by oxidation of the components of the lubricant oils.
The anti-wear additives act by formation of a solid or plastic thin film that separates the parts of the engine.
The detergent and dispersant properties the same as the reserve of basicity are in general contributed by overalkalinized additives. They are carbonates of alkaline or alkaline earth metals in a detergent solution of the sufonate, phenate, or salicylate alkyl type.
The anti-wear additives are in general sulfurized and/or phosphorized compounds, the most commonly used being the Zn dialkyl dithiophosphates.
The boron derivatives form another kind of antiwear additives. The mineral compounds of boron contribute an antiwear function and extreme pressure function (U.S. Pat. Nos. 3,907,691 and 4,100,081) while the organic compounds contribute antiwear and anti-friction properties (U.S. Pat. Nos. 4,549,975 and 4,599,183).
The incorporation of a boron compound in an overalkalinized additive will make it possible to have available a multifunctional additive having a reserve of basicity and detergent, dispersant and antiwear properties. Different methods of incorporation of the boron in an overalkalinized additive have been envisaged.
The most evident method would be to replace purely and simply the carbonic anhydride by the boric acid. This process has been envisaged in U.S. Pat. Nos. 3,853,774 and 4,601,837. But for reasons related to the difference of reactivity between the carbonic anhydride and the boric acid or anhydride, which have been pointed out in U.S. Pat. No. 3,785,976, this substitution has proved difficult.
The prior art was oriented toward boron compounds such as boric acid and the organic esters thereof, or to boron oxide which are then added to the classical previously overalkalinized additives containing calcium carbonate. Such mixtures described in U.S. Pat. Nos. 3,480,548, 4,089,790, 3,829,381 and 4,560,489 are undesirable from the point of view of their stability and their compatibility with the other additives of the lubricant formula.
In order to improve their stability, U.S. Pat. No. 3,929,650 claims the possibility of using a dispersant product of the alkenyl succinimide type.
U.S. Pat. No. 3,907,691 contemplates the formation of a complex by heating the intermediary product formed by reaction of the boric acid with the overalkalinized sulfonate. U.S. Pat. No. 4,539,126 claims the preparation of complexes by reaction of boric acid with an overalkalinized alkyl salicylate.
U.S. Pat. No. 3,928,216 indicates the use of catalytic quantities of boron salts of an amine during the overalkalinization reaction.
U.S. Pat. No. 3,679,584 suggests a mode of operation in two steps. To a classical overalkalinized additive prepared in a first step there are added in a second step the boric acid and the carbonic anhydride. But the alkaline value of the overalkalinized mixture drops very strongly during this second step, going, for example, from 295 to 177.
The alkaline value (AV) is nominally equivalent to the number of KOH milligrams per gram of overalkalinized additive tested by a strong acid. This value is determined by potentiometric dosing directly following the standard ASTM D-2896.
All the processes based on the mixture of a boron derivative with an already overalkalinized additive give products of poor stability in which the boron content and the alkaline value are equally low.
These mixtures are in general in liquid form and a of cloudy appearance. Unlike the alkaline earth carbonates that form colloidal dispersions, the boron derivatives remain in the form of coarse solid particles responsible for the cloudy appearance of the liquid. These solid particles in suspension could defeat the effect sought with the antiwear additives by causing, for example, the abrasion of the engines. When precipitating, they result in troublesome sediments and in a heterogeneity in the metal concentration.
This invention makes it possible to overcome these disadvantages and to prepare overalkalinized additives with a substantial boron content and an elevated alkaline value. Since the boron derivatives are incorporated in the globules of the colloidal dispersion, these additives are homogeneous and stable, and have very good antiwear properties.